ally smell, every
facility was given for the successful perpetration of such fraudulent
imposition. Guano, it was very soon found, varied in its composition,
but this variation in quality the farmer did not recognise. In the early
days of its use all guano was in his eyes of the same value. Too often,
as we have just pointed out, provided it had a good colour and a strong
odour, it was all right. Under such conditions, it can scarcely be
wondered at that its introduction should have proved not an unmixed
blessing to agriculture.

_Its Value as a Manure._

Guano derives its value as a manure from the nitrogen, phosphates, and
the small amount of potash it contains. This at any rate is true of the
great bulk of guano which has been used in the past. There are, as we
shall immediately see, certain kinds of guano, known as phosphatic
guanos, which only contain phosphates. The amount of such purely
phosphatic guano directly used as a manure in this country is, however,
inconsiderable, and guano may truly be described as owing its value
chiefly to its nitrogen. Not a little of its value and popularity as a
manure may be said to be due to the fact that it contains all of the
three important manurial constituents, and that in this respect it may
be regarded in a sense as a _general_ manure, thus resembling most
nearly, of all artificial manures, farmyard manure. Although its sources
are now, to a very large extent, exhausted, and its total annual imports
into this country are at present considerably less than what they were
thirty or forty years ago,[184] it may be well, on account of its
historical importance, to give a somewhat detailed account of its
origin, occurrence, and value as a manure.

_Origin and Occurrence._

Guano (which means _dung_)--or huano, as it is spelt in the Spanish
language--was first used in Peru. It seems to have been used there long
before that country was discovered by the Spaniards--probably as early
as the twelfth century. Regarding its origin there can be little doubt.
It is almost entirely derived from the excrements of sea-birds, such as
pelicans, penguins, and gulls, as well as from the remains of the birds
themselves, and of seals, walruses, and various other animals.[185]
Under the influence of a tropical sun, and in a region in which rain
scarcely ever falls, these excrements are soon dried, and remain little
changed in their composition through centuries. Many of the Peruvian
depos